The present invention relates to fiberglass manholes, and more particularly, to devices and methods for joining fiberglass manhole sections and for adjusting the elevation of fiberglass manholes.
Conventional fiberglass manholes are constructed of a cone or corbel section set on top of and fused to a bottom barrel or pipe section. The wide end of the cone section, which sits on the barrel section, and the barrel section are of equal diameter, and have straight edges which mate face to face and flush with each other. In some designs, the mating edge of the cone section has an outer lip that slides around the mating edge of the barrel section. Manufacturers contact the faces of each section together and fuse them with exterior fiberglass lay-ups. Once assembled and fused, the fiberglass manhole is delivered to the utility contractor as a one-piece unit.
Knowing the height of the one-piece structure, a utility contractor typically excavates to a depth slightly greater than the height of the manhole and sets the manhole on the bottom of the excavation so that the top of the cone section resides just below final grade level. The contractor places at least one pre-cast concrete adjustment ring on top of the cone section to properly distribute the load, e.g., highway load, across the cone section. The adjustment ring could also be made of brick. Then, the contractor places a cast iron manhole ring and cover on top of the concrete adjustment ring. Finally, the contractor backfills around the manhole to bring the grade level up to the elevation of the cast iron manhole ring.
Using a single unit manhole greatly simplifies the initial installation. However, after installation, a monolithic fiberglass manhole presents serious difficulties in adjusting the top elevation of the manhole to accommodate substantial changes in the surrounding grade level. The concrete adjustment rings on top of the cone section may be used to accommodate minor variations in grade level, typically at increments of 2 inches. However, because contractors are typically prohibited from stacking the concrete adjustment rings higher than 18 inches, or nine 2-inch rings, the concrete adjustment rings cannot be used to compensate for substantial grade level changes. Further, stacking more than three rings presents considerable drawbacks in handling and assembling the manhole structure.
Thus, to accommodate significant grade level changes, e.g., more than 6 inches, contractors are left with two options. To adjust the elevation of the monolithic fiberglass manhole, the contractor must either replace the manhole with a manhole of a height consistent with the new grade level or cut the manhole and add or subtract sections to match the new grade level.
Replacing the entire manhole requires extensive excavation and is cost-prohibitive. Cutting the manhole reduces the excavation required but creates problems in aligning and rejoining the manhole sections. Unfortunately, field conditions prevent contractors from achieving the accurate joints possible in a factory setting. Often, such attempts at field modification lead to improper joints that are not centered and not bonded well enough to prevent differential movements between the manhole sections.
The present invention is directed to a fiberglass manhole adjustment ring and a method for installing the ring in existing fiberglass manholes. The adjustment ring is installed between the cone and barrel sections of an existing fiberglass manhole that has been cut in the field.
The following definitions and descriptions are provided to clearly define the invention.
The xe2x80x9cconexe2x80x9d or xe2x80x9ccorbelxe2x80x9d is the upper section of the manhole that is positioned with the narrow opening at the top and the wide opening at the bottom. The narrow opening is set just below grade level and receives the concrete adjustment rings and manhole ring and cover. The wide opening joins the lower section of the manhole structure.
The xe2x80x9cpipexe2x80x9d or xe2x80x9cbarrelxe2x80x9d section is the lower section of the manhole that is open on one end and closed on the other end to form a container. The open end joins the cone section.
A xe2x80x9cself-centering lipxe2x80x9d is a strip of fiberglass material adhered to the full circumference of an interior or exterior edge of a manhole section. The lip extends from the edge of the manhole section to form a collar in the case of an exterior lip or a sleeve in the case of an interior lip. An exterior lip fits around an adjoining manhole section, while an interior lip slides into an adjoining manhole section.
In light of the above definitions, the fiberglass manhole adjustment ring includes a section of fiberglass pipe with an interior or exterior self-centering lip attached to one or both ends of the pipe. The diameter of the fiberglass pipe is equal to the diameter of the barrel section. The length of the pipe is dependent upon the required change in elevation of the manhole.
The length and thickness of the interior or exterior lip depend upon the diameter of the adjustment ring and the pipe section. The larger the diameter, the greater the possibility of high lateral forces, and the thicker and longer the lip has to be. The lip must provide a tight, centered fit to resist any movement between the manhole sections.
Depending upon the type of construction of the existing manhole, self-centering lips may be needed on both sides of the adjustment ring. If the originally manufactured cone and barrel section of the manhole are joined without self-centering lips, then both sides of the adjustment ring must be fitted with any combination of interior and exterior self-centering lips. In this manner, when the cone and barrel section are cut and separated, they are rejoined by sliding the lips on either side of the adjustment ring into or around both the cone and barrel sections. If either the cone or barrel section was manufactured with a self-centering lip, a self-centering lip on the adjustment ring is unnecessary because the adjustment pipe section, matching the original diameter of the cone or barrel section, will slide inside or around the original self-centering lip.
Turning to the method of installation, a contractor first cuts the factory-applied exterior fiberglass lay-up located where the barrel and cone sections meet. The cut must be just deep enough to sever the lay-up and allow removal of the cone section. If the existing manhole was manufactured with an exterior self-centering lip, the contractor uses that lip as a guide to cut through the exterior lay-up. After cutting the lay-up and removing the cone section, the contractor installs the manhole adjustment ring by sliding the ring self-centering lip around or inside the exposed barrel section. The contractor then sets the original cone section on top of the adjustment ring to complete the re-assembly. Finally, the contractor bonds the sections together with, e.g., fiberglass lay-ups on the exterior manhole surface centered over each new joint.
One skilled in the art would readily understand how to use multiple adjustment rings in varying heights to reach a desired elevation. Further, varying constructions of existing manholes would necessitate multiple combinations of adjustment ring end fittings, i.e., interior or exterior self-centering lips. Also, various means of attaching the self-centering lip to the adjustment ring are possible, e.g., pop rivets, bolts, and fiberglass molding that allows for the use of a rubber, cork, or caulk gasket. Finally, any number of methods of bonding the sections could be used to satisfy site condition requirements or municipal specifications, e.g., molding a self-centering lip channel that allows adhesive to be placed in the channel, using epoxy, using adhesives, applying shrink-wrap, or clamping a rubber gasket in place with worm drive clamps.
In another embodiment of the present invention, self-centering lips are provided on manhole sections to enable a contractor to erect a manhole in the field, as opposed to receiving a factory assembled single-piece unit. In this manner, a contractor sets the barrel section, connects and grouts the pipe entering the barrel section, and grouts the invert inside the base of the barrel section before the remaining manhole sections are set on top of the barrel section. With the aid of self-centering lips, the sections are joined using the same method for installing the fiberglass manhole adjustment rings. A preferred mode of joining and bonding the manhole sections uses a fiberglass adhesive channel and self-centering lip molded to the interior or exterior top edge of the barrel section. As an alternative to the fiberglass adhesive channel, other preferred embodiments bond the sections using a shrink-wrap, a rubber gasket with clamps, an epoxy, or an adhesive.
Allowing the contractor to assemble the manhole in the field avoids the confined-space work otherwise required by conventional single-piece fiberglass manholes. With single-piece fiberglass manholes, contractors must set the manhole and descend into its narrow confines to connect the pipe and form the invert. This confined-space work deep within the manhole burdens the contractor with the cost of providing safety equipment, e.g., tripods, harnesses, and respiratory protection, and the cost of reduced productivity in implementing safety procedures. To eliminate these added costs, the manhole sections with self centering lips allow the contractor to lean over the edge of the barrel section and complete the pipe and invert work from the outside, before the remaining manhole sections are joined to the barrel section.
Accordingly, it is an object of the present invention to provide a device and installation method that facilitates easy adjustment of the height of an existing fiberglass manhole without compromising the quality of the manhole construction.
It is another object of present invention to provide a device and installation method that facilitates field assembly of a fiberglass manhole.
These and other objects of the present invention are described in greater detail in the detailed description of the invention, the appended drawings and the attached claims.